Locked or partially locked handbrake function causing the brake shoes to rub on the inner drum. In many cars the handbrake function is separate to your rear brakes, so it's not always clear that's the problem. Try jacking up the rear wheel (safely obvs) to see if the wheel spins freely with the handbrake off. If there's any friction or its hard to spin you have your answer. Either way hot + smelly ain't great so suggest parting with a few SATs to fix it quickly.